This disclosure relates to a device for safeguarding a monitoring area in which an automatically operating machine is arranged, having a camera system for monitoring the monitoring area, a configuration unit for defining at least one protection area within the monitoring area, and an analysis unit for triggering a safety-related function.
The disclosure furthermore relates to a corresponding method and computer program for safeguarding a monitoring area in which an automatically operating machine is arranged.
In the case of modern industrial robots, which move at significant speeds, collisions generally result in severe damage, both to the robots and also to the workpieces handled thereby. This can result in costly production outages. The safety of persons who interact with the automatically operating robots also has the highest priority. In the case of modern industrial robots and other machines having moving machine elements, the movement of which represents a hazard to persons and other objects, a collision between the moving machine elements and a foreign object therefore has to be prevented by protection units. For this purpose, it is usually sufficient to bring the machine to a standstill before an undesired contact occurs.
Traditionally, hazardous areas around automatically operating machines are safeguarded using mechanical barriers in the form of protective fences and protective doors or with the aid of light barriers, light grids, and laser scanners. The light barriers, light grids, and laser scanners are frequently also used in combination with the first-mentioned mechanical barriers. As soon as a person opens a protective door or interrupts a light grid or a light barrier, a shutdown signal is generated, and the hazardous operating movement of the machine is stopped, or the machine is brought into a safe state. However, the installation of such protective units is quite complex and the protective units require a large amount of space around a hazardous machine. In addition, such protective units are less flexible when it is important to adapt the safeguarding of the hazardous operating area to different operating situations of the machine.
In particular in the case of optoelectronic sensors, such as light grids, light barriers, or reflected light sensors, undesired shutdowns of the machines or facilities can occur. Extremely small parts or interfering lights, which would actually be harmless with regard to safety technology, nonetheless can trigger the shutdown signal. This frequently results in unnecessary restrictions of the machine and facility availability, since a shutdown also takes place in situations which are harmless from a safety-technology viewpoint. Attempts have therefore been made to filter out interfering objects and interfering lights in the case of light grids, light barriers, or reflected light sensors. One known technology is that the light emitter emits bit-coded light signals, which are decoded by the receiver and compared to target values. In the case of reflected light sensors, inter alia, polarized light is used. Even mirrors or bright objects are thus still detected as a beam interruption.
A further known technology is known from DE 202 12 769 U1. DE 202 12 769 U1 discloses a light grid, which analyzes a predefined number of multiple scanning cycles with respect to the occurrence of beam interruptions of beam axes to generate an object determination signal. This is used to suppress transient interference. Smaller, irrelevant interfering objects such as insects, pollen dust, woodchips, and sawdust can be suppressed by so-called multiple analyses. This corresponds to a time filter, which tolerates an interruption of the protection area or parts thereof for a defined time, since it is presumed that interfering objects only occur temporarily. It is disadvantageous in this case that “real” infringements are also not detected in this time, i.e., in fact this results in lengthening of the reaction time and therefore in greater safety distances. In addition, this is made more difficult in that interfering objects not only appear temporarily, but rather are certainly also present for a longer time. In this case, the time filter does not help, so that the optoelectronic sensor would nonetheless recognize an infringement and accordingly generate a shutdown signal.
To avoid the above-mentioned disadvantages, efforts have been made for some time to implement the safeguard of the hazardous operating area of an automatically operating machine with the aid of camera systems and suitable image processing. Such a system is sold by the applicant under the name “SafetyEYE”. It is a characteristic of such camera systems that, in contrast to normal cameras, even if a malfunction occurs, a secure state of the machine or facility which causes hazard has to be ensured. The use of camera systems also has the advantage that volumes instead of individual lines or surfaces can be safeguarded. Such camera systems specifically enable three-dimensional protection areas to be virtually monitored from all sides. It is therefore possible to again increase the safety and to monitor continuously.
EP 1 543 270 B1 describes such a system having at least two cameras, which cyclically supply images of the hazardous operating area. The images of the cameras are analyzed using at least two algorithmically different methods, wherein the hazardous operating movement of the machine is stopped or is brought into a safe state if at least one of the two methods supplies a foreign object detection in a previously defined protection area. Each of the two analysis methods generates items of 3D information from the images of the cameras, so that the position of objects in the defined protection area can be established with the aid of the method. A significant demand on such methods and devices is that the image processing, which is complex in any case, has to be implemented so it is failsafe in the meaning of relevant standards for machine safety, in particular EN ISO 13849-1, IEC 61508, EN ISO 13855, and IEC 61496, so that such a device can actually also be used for safeguarding a hazardous machine. A failure of the device itself cannot have the result that the safeguard of the machine is lost. Failsafe in this meaning is therefore considered to be a device which reaches at least SIL 2 according to IEC 61508 and/or performance level PL (d) according to EN ISO 13849. The method known from EP 1 543 270 B1 and a corresponding device can provide this and have already proven themselves in practical uses.
In the last-mentioned camera-based security systems, virtual protection areas are usually defined around the machine. The camera system detects whether a foreign object penetrates into such a protection area and thereupon turns off the machine or the facility, or brings it into a secure state. The problem nonetheless also exists in these systems that the movement of the machine or facility which causes danger is sometimes stopped without an apparent reason, which results in a shutdown of the production facilities and in production breakdowns. This can be because of extremely small parts, for example, which penetrate into the virtual protection areas, are detected as foreign objects, and therefore trigger the safety-related function. This is not desirable in particular in the case of very short cycle times and long interlinked production lines, which are to be found in particular in the automotive industry.
DE 102 51 584 A1 proposes such a camera-based safety system and associated method, in which the safety is to be increased by optimized image processing. For object acquisition, image features of current camera images are compared to a reference image feature of a stored reference background. The mentioned reference background has to be referenced in this system in a learning phase or a so-called teach-in procedure. According to the proposed method, a valid reference background is only provided if, upon the check of the reference background in both computer units, it is obtained in correspondence as a result that no adjacent zones having the same reference image feature are present within the reference background. This teach-in procedure can therefore be relatively boring and cumbersome. During the subsequent image acquisition of the protection area, the image features of the camera images are differentiated into safety-critical and non-safety-critical objects. The safety-critical objects include the operators, preferably the arms of an operator. Non-safety-critical objects are formed, for example, by static objects in the surroundings of the machine or facility, in particular also the parts to be processed thereby. If the comparison of the image features to the reference background does not result in a corresponding result, the operating means is also taken out of operation for safety reasons, since it cannot be precluded in this case that a safety-critical object is located in the protection zone. Extremely small parts which could be noncritical, but are not imaged in the reference background, would thus also result in an undesired shutdown of the machine or facility in the case of this system. The above-described problem of undesired restrictions of the machine or facility availability is thus also only partially solved by this method.